Without the battery, the remote won't disarm the security system (which automatically re-arms itself). Without the security system disarmed, the car won't start. Without starting, the car won't drive. Without the capability of driving the car, I'm grounded but for the feet and the bus and the kindness of local associates for the nonce.
It's the little things in life that make you appreciate the big things.
(The battery waited to die until I was home and not going anywhere other than work for just a bit.)